The present invention is in the field of turbomachinery and, more particularly, turbomachinery which may be susceptible to surface icing with particular applications of aircraft propellers.
Certain components of turbomachinery may be subjected to a flow of cold, moisture laden air which may produce an undesirable formation of ice. One example of such a component may be a nose cone of an engine of an aircraft. To counteract formation of ice, nose cones may be provided with integral heating systems.
Various heating systems have been described in the prior art. An electrical heating system is described in U.S. Pat. No. 6,503,056 (Eccles et al. Jan. 7, 2003). In this system an engine is provided with an integral generator that may produce power to energize an electric heater in a nose fairing of an aircraft. In U.S. Pat. No. 5,573,378 (Barcza, Nov. 12, 1996), nose cone deicing may be provided when compressor bleed air is applied to a plenum that surrounds an inlet of an engine. In these prior art deicing systems, engine performance is diminished. When energy is consumed in the production of bleed air or electrical heating it is not available to produce forward thrust for aircraft propulsion.
Some prior art attempts have been made to perform deicing without adversely effecting engine performance. One such prior-art method employs engine lubricating oil as a heat source for nose cone deicing. In this prior-art method, oil which may be normally circulated into bearings and gearing of an engine may become heated during its normal lubricating function. The heated oil may then be directed to a nose cone where some of the latent heat of the oil may heat the nose cone. In a typical prior-art heating system, the oil may be passed through serpentine tubing in contact with various portions of the nose cone.
This engine-oil deicing method may be advantageous in that it ostensibly may not diminish engine performance. It may use heat that is inherently produced by the engine from its normal operation. Nevertheless when engine oil flows through the prior-art de-icing systems, a high pressure drop may be produced in the oil flow. This may be due to various factors. For example, a de-icing system that utilizes serpentine tubing may require oil to flow over a very long path with a high velocity as it travels through the tubing. Typically the tubing is positioned to cover substantially the entire outer surface of a nose cone to insure intimate contact with the areas on which ice may form. This lengthy travel may produce a high pressure drop.
In addition, air may become entrained in the oil when it passes through bearings and gearing. In some cases, an air-oil mixture emerging from bearings and gearing may comprise 5 parts air to one part oil. A mixture of air and oil may be an ineffective heat transfer medium to insure proper heating of the surfaces. As the air-oil mixture flows though heat transfer passages, the air may become the predominant heat transfer fluid because the air may migrate radially outwardly and produce ineffective cooling. Also, a mixture with a high volume of air may experience a high pressure drop during its transit through the passages. A high pressure drop in the air-oil mixture may present a need to provide additional oil pump pressure. Producing such additional pressure may require added energy and thus may contribute to diminished engine performance. Additionally, if some of the air can be separated from the mixture before re-introducing the air-oil mixture into the bearing location, some improvement in lubricating action may beneficially occur.
As can be seen, there is a need to provide a deicing system that may operate without diminishing engine performance. Additionally, there is a need to provide an engine-oil deicing system in which entrained air is not the predominant heat transfer medium.